Spray guns are widely used in vehicle body repair shops when re-spraying a vehicle that has been repaired following an accident. In the known spray guns, the paint is fed to a spray nozzle from a reservoir attached to the gun. On emerging from the spray nozzle, the paint is atomised and forms a spray with compressed air supplied to the nozzle. The paint may be gravity fed or, more recently, pressure fed by an air bleed from the compressed air line into the reservoir.
A typical reservoir consists of a paint pot having an outlet in the bottom of the pot that is attached to the spray gun and a removable cap at the top by means of which paint can be introduced into the pot for delivery to the spray gun.
With this arrangement, the spray gun and pot have to be thoroughly cleaned when changing the paint in the reservoir to avoid cross-contamination which may adversely affect the finish. This is especially important when spraying part of a vehicle to match exactly the colour of the existing colour of the adjacent bodywork.
Cleaning is time consuming and involves the use of solvents that can give rise to health and/or safety hazards. A typical finish may require application of a primer, base coat and a clear lacquer. The spray gun and pot may therefore have to be cleaned several times when carrying out a single repair and this increases considerably exposure of the operator to the health and safety risks associated with such cleaning.
Furthermore, cleaning adds significantly to the repair costs in terms of both the working time lost while the spray gun and pot are being cleaned and the costs of the cleaning materials themselves and/or any paint remaining in the pot that is thrown away.
In order to reduce the amount of cleaning and to facilitate changeover from one paint to another, we have previously proposed in WO 98/32539 an arrangement in which a paint pot is provided with a separate, open-topped liner for the paint to be dispensed. The liner is a close fit in the pot and is closed by a separate lid that has the outlet for releasable connection to the spray gun.
In use, the liner collapses as paint is withdrawn and, after spraying, the liner and lid can be removed allowing a new, clean liner and lid to be employed for next use of the spray gun. As a result, the amount of cleaning required is considerably reduced and the spray gun can be readily adapted to apply different paints in a simple manner.
This has considerable benefits for the user. In particular, efficiency is improved by reducing the amount of working time lost while changing over the spray gun to spray another paint and exposure of the operator to the potential health and safety risks associated with the cleaning operation are lessened by reducing the amount of cleaning materials required. This can result in cost savings for the user.
A problem can arise, however, if there is any paint remaining in the liner when the lid/liner assembly is removed from the paint pot. It is often not practical to transfer any unused paint from the liner to a storage container and throwing the lid/liner assembly away with unused paint is wasteful and a potential health/safety hazard from leakage of the paint.
Storage of any unused paint in the liner is possible by temporarily closing the outlet in the lid, for example with a cap. This may allow the liner and lid to be re-fitted in the paint pot for use of the remaining paint. However, this is generally only suitable for short term storage of up to a few hours. Thus, over a longer period of time, the cap may become stuck to the lid by drying paint making removal of the cap difficult or preventing removal altogether. In addition, there is a risk of contamination of the paint by flakes of dried paint breaking away and falling into the paint if the cap is forcibly released.
Further problems for long term storage of unused paint result from the instability of the liner/lid assembly when the liner is in a collapsed condition and from the susceptibility of the fragile liner/lid assembly to damage if dropped or otherwise mishandled. Thus, there is a risk of leakage, spillage of paint if the lid and liner become separated making storing and handling of the liner/lid assembly for any appreciable time complicated.